1. Field of the Invention
This invention relates to semiconductor material processing and in particular to III-V semiconductor material processing.
2. Art Background
Low temperature alternatives to conventional chemical vapor deposition processes have been sought for the deposition of materials such as III-V semiconductor thin films utilized in a variety of device fabrication procedures. Low temperature processes, i.e., processes involving temperatures lower than 500 degrees C., offer the advantage of allowing deposition of a film without substantially affecting previously deposited layers containing materials that undergo compositional and/or phase changes at relatively low temperatures.
One approach being pursued in an attempt to achieve low temperature deposition involves the use of photo-stimulated techniques. In these techniques, electromagnetic radiation from a source such as a laser or a high intensity lamp is utilized to induce a chemical reaction in a gas that is present at the substrate upon which deposition is desired. Such radiation induced processes have fallen generally into two categories. In the first category, an ultraviolet lamp has been utilized in attempts to induce dissociation in a deposition gas, e.g., a metal organic compound, through photodecomposition to produce semiconductor material. However, as reported by Aylett and Haight (Materials Research Society Symposium, Boston, November 1982, paper I5.4), the use of an ultraviolet lamp in conjunction with organometallic materials such as (CH.sub.3).sub.3 InP(CH.sub.3).sub.3 leads only to the formation of indium droplets or alternatively to indium phosphide whiskers.
In a second approach directed to the deposition of III-V materials, a laser such as a Nd-YAG laser (532 nm) is utilized to irradiate a substrate in the presence of a deposition gas such as a composition including trimethyl gallium and arsine (AsH.sub.3). The laser is chosen so that its wavelength intensity is centered at energies that are not absorbed by the gas but that are instead absorbed by the substrate to produce surface heating. This heating, as reported by Roth et al (Materials Research Society Symposium, Boston, November 1982, paper I6.2), pyrolyzes the trimethyl gallium and the arsine, resulting in gallium and arsenic entities that combine to form a gallium arsenide deposit. Although by this approach gallium arsenide, rather than gallium droplets, is obtained in deposition regions substantially larger than whisker size, the process induces substantial substrate heating and in fact is essentially the same as other high temperature approaches. Thus, although there are processing advantages potentially available through the utilization of photo-stimulated processes, the procedures pursued have not yielded satisfactory results for III-V materials or are, in fact, not low temperature techniques.